Support for same-sex marriage in California has never been higher, with 59 percent of the state's voters backing the legalization of gay nuptials, according to a new Field Poll.

What's notable is that some of the more significant gains in support came from Catholics, Latinos and older voters - part of the core of support for voter-approved Proposition 8, the 2008 ballot measure that defined marriage as between a man and a woman.

Republicans and those who identify themselves as conservatives are the only demographic blocs that oppose allowing gays to marry, according to the survey of 1,003 registered voters released today. Overall, 34 percent of the respondents oppose same-sex marriage.

In a separate question, 51 percent of respondents said gays should be allowed to marry - up from 44 percent two years ago. The survey found that 29 percent support civil unions but not marriage and 15 percent favor no legal recognition. Five percent had no opinion.

"It's a wholesale change in public opinion," said Field Poll Director Mark DiCamillo, noting that Field has polled on same-sex marriage issues since 1977. "Right now, it is more of a political objection than anything else."

Wary of numbers

But the rise in support was so high in this poll - seven points since the last Field survey on the issue in 2010 - that even some supporters of same-sex marriage are wary.

A September survey of likely voters commissioned by Equality California, which has been at the forefront of the fight for same-sex marriage, also found that 51 percent of Californians support it.

"While progress has been made, support does not yet appear to be sufficiently high enough to provide a solid opportunity for a successful ballot measure campaign on same-sex marriage in California," said an Equality California memo on Tuesday.

Rebekah Orr, communications director for the group, added, "While we welcome news that public opinion is changing, we know that public opinion is still pretty much in flux."

Opponents were even more skeptical of the poll's results, noting that there's a huge gulf between what voters tell pollsters and what they do in the voting booth. Voters have never approved same-sex marriage in the nearly three dozen times the issue has appeared on state ballots nationwide.

"They can take polls all day long," said state Sen. Doug LaMalfa, R-Richvale (Butte County). "California has its own distorted view of the world, but on this issue I think the voters have been very consistent."

Accelerating shift

Still, the new Field survey shows that a generational shift in attitudes among older voters is accelerating, particularly among people of color who tend to be more conservative on social issues such as marriage.

For years, people on both sides of the issue have acknowledged that support for same-sex marriage would increase over time as older voters, who overwhelmingly oppose gay nuptials, died.

But the survey found that 65 percent of nonwhites under 40 - most of them Latino - support same-sex marriage. Fifty percent of nonwhites over 40 oppose same-sex marriage, DiCamillo said.

Four years ago, 64 percent of Catholic voters supported Prop. 8, according to exit polls. But Field's latest survey found that 51 percent of Catholics support same-sex marriage.

Impact of the courts

DiCamillo attributed this spike in support in part to a series of court rulings in favor of same-sex marriage. This month, the Ninth U.S. Circuit Court of Appeals in San Francisco declared California's voter-approved ban on same-sex marriage unconstitutional. Should the Supreme Court decide to review the matter, it probably won't happen until 2013.

Two federal courts, including one this month in San Francisco, have declared the federal Defense of Marriage Act, which defines marriage as between a man and woman, unconstitutional. In recent weeks, state legislators in Washington and Maryland have approved laws to make same-sex marriage legal in their states.

But those gains may not last long. Voters in as many in five states will vote this year on whether to legalize same-sex marriage.